1. Field of Invention
The present invention relates to a syringe which makes it possible to qualitatively visualize the pressure of fluids such as blood, and to a catheter set comprising said syringe.
2. Description of Related Art
When a catheter or guidewire is inserted into a blood vessel in a human or other body, the practitioner first of all ensures that the intended blood vessel (vein or artery) has been identified using a syringe which has a puncture needle fitted to the tip end. When a central venous (CV) catheter is made indwelling, for example, the subclavian vein or internal jugular vein is punctured using a cannula which can remain indwelling in a blood vessel (a puncture needle surrounded by a tube). When a blood vessel lying deep within the body is to be punctured, it is not possible to ascertain the position of the blood vessel or where it runs either visually or by palpation, and a practitioner such as a specialist physician will use his or her anatomical knowledge and experience to establish the puncture site and puncture direction. The only information at the practitioner's disposal when the blood vessel is identified is the slight feeling transmitted to the fingers when the tip of the puncture needle passes through the wall of the blood vessel and the return flow of blood.
Considering that the slight feeling when the tip of the puncture needle passes through the wall of the blood vessel is often eliminated by the pressure produced when the needle passes through the subcutaneous tissue and muscle which runs from the skin to the blood vessels, that this feeling is momentary and that it is easy to make mistakes on a subjective decision, the return flow of blood is considered to be the only reliable source of information. It is possible to establish whether the tip of the puncture needle attached to the end of the syringe is inside a blood vessel using the return flow (flash-back) of blood into the syringe barrel as a source of information.
The blood vessels lying deep inside the body are characterized by arteries and veins which run side-by-side, for example arteries lying close to or behind veins. The internal jugular vein runs parallel to the common carotid artery and the subclavian vein runs parallel to the subclavian artery, for example. The way the blood vessels run also varies from person to person, and it cannot be said that establishing a puncture site and puncture direction using the anatomical knowledge and experience of a practitioner is entirely without error. A practitioner therefore needs to correctly judge whether the blood vessel which has been punctured is a vein or an artery using information obtained from the return flow of blood.
In a medical setting it is also necessary to reliably establish in a short time that a vein rather than an artery has been punctured when a catheter or guidewire is inserted into a vein. That is to say, the patient needs to be treated swiftly and correctly in the medical setting for reasons of urgency and health, and it is important to be able to establish both quickly and accurately whether the blood vessel punctured by the puncture needle is indeed the intended blood vessel. It is nonetheless difficult to establish at a glance whether the blood vessel punctured by the puncture needle is the intended blood vessel, even for an experienced physician.
Standard methods of establishing whether the blood vessel which has been punctured is a vein or an artery from the return flow of blood involve determining any of the color of the aspirated blood, the oxygen saturation of the blood, or the blood pressure. When the blood vessel is identified by the color of the blood, it is possible to judge that it is an artery if the color of the blood is bright red and that it is a vein if the color of the blood is dark red. When the blood vessel is identified by the oxygen saturation of the blood, it is possible to judge that it is an artery if the oxygen saturation is high and that it is a vein if the oxygen saturation is low. When the blood vessel is identified by the blood pressure, it is possible to judge that it is an artery if the blood pressure is high and that it is a vein if the blood pressure is low.
When the blood vessel is identified by the color of the blood, it may be the case that the blood is not bright red, even if the blood vessel is an artery, because the patient's respiration becomes shallower when a general anaesthetic is in full effect, for example. Furthermore, if the oxygen partial pressure from an oxygen mask is high, the oxygen saturation in the blood also increases, and it may be the case that the blood comes close to being bright red even if the blood vessel is a vein. In addition, the color of the blood varies from person to person, and it is not the case that blood color is constant. For these reasons, the color of the blood is not fixed due to individual differences and the state of the patient at the time, and therefore the color of the blood is not a reliable indicator for identifying the blood vessel.
There is a correlation between the oxygen saturation and the color of the blood, and therefore when the blood vessel is identified by the oxygen saturation, the difficulties in making this determination in the case of blood color also apply to the determination in the case of oxygen saturation. Additional measuring equipment is also required in order to measure the oxygen saturation of the blood. Identifying the blood vessel by the oxygen saturation of the blood is therefore problematic in that is an impractical method because of the need to prepare separate measurement equipment, the complexity of the operation entailed by the measurement, and the time taken to obtain the measurement results, among other things.
On the other hand, it is possible to determine whether the blood vessel which has been punctured is a vein or an artery in a short time and with a greater degree of accuracy by utilizing the difference in blood pressure between arteries and veins. Technology has therefore been proposed for determining whether the blood vessel which has been punctured is an artery as, for example, in German Utility Model Application 920810, hereinafter DE 9208103. Technology has also been proposed which makes it possible to determine whether the blood vessel which has been punctured is a vein or an artery in a short time and with a greater degree of accuracy by utilizing the difference in blood pressure between arteries and veins as, for example, in Japanese Unexamined Patent Application Publication H10-165509 hereinafter JP 165509.
The technology disclosed in DE 9208103 involves attaching a display device 20 after the puncture has been made, rather than before or when the puncture is being made. When a blood vessel is punctured, the venous pressure is generally 2-8 mmHg, and therefore it is not possible to produce a return flow of blood unless there is negative pressure in the syringe when the puncture is being made. With the technology disclosed in DE 9208103, if it becomes necessary to provide negative pressure in the syringe and recheck whether the tip of the needle is in a blood vessel, the negative pressure is corrected once the device has been removed and then it is reattached, which leads to a complicated operation and procedure.
Furthermore, the operation to attach the display device 20 follows the confirmation of the blood vessel, and therefore there is a possibility that the subsequent attachment operation will cause the tip of the needle to become misaligned with the blood vessel which has at last been confirmed, and that the tip of the needle will be removed outside the blood vessel (for example, the needle will pass through the front wall or rear wall of the blood vessel, or the needle will come out from the blood vessel, etc.).
In addition, it is not generally possible to visually identify a blood vessel lying deep within the body, and therefore the operation to identify the blood vessel is normally repeated a number of times, since there is not really any expectation that the intended blood vessel can be identified in a single operation. If it proves impossible to identify the intended blood vessel, the blood etc. which has flowed into the syringe is discarded and the operation to confirm the blood vessel is carried out once again. However, with the technology disclosed in DE 9208103, there is a risk that the blood to be pushed out will head not towards the tip of the needle but towards a branch pipe 14, and even if only a small amount of blood etc. remains in the display device 20, it is necessary to prepare a new display device 20 once again. The technology disclosed in DE 9208103 is therefore not considered to be suitable for multiple blood vessel identification operations.
The technology disclosed in JP 165509 makes it possible to determine whether the blood vessel which has been punctured is a vein or an artery in a short time and with a greater degree of accuracy by utilizing the difference in blood pressure between arteries and veins. While this technology does have some advantages, there is a need to develop a syringe that is more easily used in practice, in addition to the need for further improvements in terms of usability, compactness, hygiene and cost etc.
The present invention has been devised in order to resolve the issues outlined above, and it aims to provide a syringe which utilizes the difference in pressure in fluids such as blood and which makes it possible to identify the target in a short time and with accuracy by qualitatively visualizing the pressure of said fluids; the invention also aims to provide a catheter set comprising such a syringe.